It is important to balance tire on vehicles and the importance of balancing tire weight increases with the size or the vehicle and the size of its tires. Even though tires may appear identical, variations in their manufacture invariably produce tires whose weight is unevenly distributed around the circumference of the tire. Unless this unequal tire weight is counterbalanced, tires vibrate during operation and the vibrations will sharply reduce tire performance and longevity.
A conventional method for balancing tires uses wheel weights fixed to rims of the wheels that support tires. Common lead/lead/alloy wheel weights are bonded to a piece of steel for rigidity and for installation mounting purposes. When this steel portion comes in contact with modern aluminum alloy wheels, the softer aluminum alloy is scratched and abraded, and eventually will result in corrosion due to the interaction of two dissimilar metals. If the alloy rim has had a factory protective coating installed, the installation of the wheel weight will remove this coating, allowing road salt to corrode the metal and other contaminants to seep under the coating.
These wheel weights are unsightly on modem, expensive, alloy rims. Moreover, wheel weights are only effective until the imbalance point changes. Imbalance points change over time due to normal wear, panic stops, or accelerated, uneven wear due to load and road condition variations. Any of these conditions can, and normally do, cause the imbalance position to change. This is why most tire manufacturers recommend rebalancing the tires two to three times throughout the life of the tire. In the real world, however, most people only have their tires balanced once at the time of installation. As a result, most vehicle owners experience less tire mileage than they could actually obtain if they had a system to maintain the balance in their tires.
Wheel weights can fall off, or be knocked off if a person runs into a curb. It is not uncommon for small clumps of dirt, debris, or snow to get caught on the inside rim of the tire. The original tire using weights was balanced without this additional weight, and so is now out of balance. As long as the additional weight does not exceed the capacity of the amount of beads in the tire, the beads will shift their position to try to correct for the new imbalance. Standard wheel weights cannot do this without being removed, and the entire assembly rebalanced.
Others have addressed the drawbacks inherent in wheel weights by providing tire balancing material inside a tire. For example, an early attempt at a self-balancing fire is found in U.S. Pat. No. 2,909,389. That patent describes how weights are placed in a tube contained in a tire. When the wheel rotates the weights are thrown against the inner surface of the outer wall of the tube and the imbalance of the wheel is said to be corrected by the position assumed by the weights. Later patents describe self-balancing powders, glass beads or steel beads. See, for example, U.S. Pat. No. 6,249,971 (polymer) and U.S. Pat. No. 6,128,952 (glass) and U.S. Pat. No. 4,179,162 (steel, ceramic, or rubber cylinders).